What are the connotations of "Panim be'Fanim Diber Hashem ... "?
1.
Rashi: Yisrael should not say that Moshe tricked them with the Aseres ha'Dibros, in the way that an agent tricks a purchaser into buying the article he is trying to sell on behalf of the seller, since they heard them directly from Hashem.
1
2.
Seforno: To remind them that at Har Sinai, Hashem did not reveal Himself to them via a dream or a vision,
2
but Face to face.
3
In the way that He appeared to Moshe Rabeinu. See Ve'zos ha'Berachah, 34:10.
2)
Why does the Torah mention the fact that Hashem spoke to Yisrael Face to face here and not by Matan Torahi?
1.
Oznayim la'Torah: Because it also contains a hint of a rebuke - in that, at Har Sinai, Yisrael saw Hashem Face to faace, whereass now, after the sin of the Golden Calf, they were not even able to look at the face of Moshe.
1